In the international system, deterrence and its defensive deterrence instances are considered among the major issues of national security. Therefore, to achieve stability and security, governments have to design and develop various defensive systems, missiles, aircraft, warships, and other advanced military equipment. This paper, by a descriptive-analytical method and using library resources, reviewing reputable scientific sites related to the S-300PMU-2 family missile system, aimed to explore the effects of the S-300PMU-2 air defense system on the defensive deterrence of the Islamic Republic of Iran. We also investigated the extent to which it provides defensive coverage for Iran. Accordingly, the researcher persuaded various goals in dimensions determining the concept of deterrence based on air defense system, security, geographical scope, and fighters in the scope of the system. The obtained findings revealed that the missile system presented a relatively high level of defense of the country at domestic and regional levels. It also was able to fight fourth-generation fighters and ballistic missiles. The general results of the research indicated that the defensive system of the Islamic Republic of Iran, despite the evolutionary process, requires to be upgraded. The S-300PMU-2 air defense system, as one of the most essential links in the evolution of the current air defense model of the country, can repel the threats of the country at the regional level. It can also upgrade the country’ s defense system to the continental and global levels; however, there is a need to use new weapons in the future.